This invention relates to a motor which provides continuous rotary output from the oscillating movement of linear actuators.
There are many applications for lightweight, low speed, high torque motors which can be reversed or locked up almost instantaneously. One such application is in the activation of flaps, speedbrakes and other control surfaces on aircraft. While hydraulic actuators work well in these applications they are costly and heavy, both of which are extremely undesirable in aircraft, particularly in general aviation aircraft. In addition, hydraulic actuators require the use of extensive hydraulic lines which create maintenance problems and are subject to failure. Thus, electric motors are preferable for this purpose in general aviation aircraft.
However, heretofore electric motors have had several shortcomings when used for actuating aircraft control surfaces. While electric motors themselves are lightweight, they generally are high speed and must be geared down to obtain the torque necessary to overcome the aerodynamic forces they encounter in this application. The resulting gear boxes are heavy, and, in addition, have a considerable amount of inertia. Thus, it is difficult to stop or reverse them quickly. In addition, the gears used in reduction gear boxes are susceptible to breakage if the device becomes jammed.
The present invention overcomes the foregoing shortcomings of the prior art electric motors by providing a lightweight electric motor which is capable of low speed, high torque operation without the necessity of substantial gearing. This is accomplished by placing a pair of linear actuators with their actuation elements facing one another in axial alignment. The actuation elements of the actuators are connected to opposite ends of a rack gear. Thus, if the actuators are alternately activated, to pull their actuation elements towards them, the rack gear oscillates back and forth. A pair of sector gears, which are rotatably mounted on shafts having axes which are normal to the axis of the rack gear, engage the rack gear and rotate back and forth as the rack gear oscillates.
Each of the sector gears is coupled to its respective shaft through a one-way clutch, however, one of the clutches engages only to transmit clockwise rotation and the other engages only to transmit counterclockwise rotation. Each of the shafts also has a drive gear mounted on it and the two drive gears mesh together. As a result the two drive gears must rotate counter to one another.
An idler gear, which is mounted on a solenoidactuated carrier, can be positioned to engage either one of the drive gears. The idler gear also engages an output gear which serves to transfer the output of the motor to the device being powered by it.
When the rack gear is moving in the direction which causes the sector gears to rotate counterclockwise the first sector gear, which is coupled to its associated first shaft through the counterclockwise engaging clutch, causes the first shaft, and thus the first drive gear, to rotate in a counterclockwise direction. Since the two drive gears intermesh this causes the second drive gear to rotate in the opposite or clockwise direction. This is possible because the counterclockwise rotation of the second sector gear is not being transferred to the second shaft by its one-way clutch. When the direction of the rack gear is reversed the sector gears are rotated in a clockwise direction. The second sector gear now is coupled to the second shaft through the clockwise engaging second one-way clutch, and thus the second drive gear continues to rotate in a clockwise direction. The clockwise rotation of the second drive gear then keeps the first drive gear rotating in the same counterclockwise direction. As a result, as long as the idler gear remains engaged with the same drive gear the output gear rotates continuously in the same direction when the rack gear oscillates.
However, the direction of the motor can be reversed simply and quickly by moving the idler gear out of engagement with one drive gear and into engagement with the other drive gear. Since reversal is accomplished without interrupting operation of the motor, there is little momentum to overcome and reversal can be accomplished quickly without creating stress on the motor parts. Likewise, the motor can be stopped almost instantaneously without creating any stress greater than that which occurs during continuous operation merely by discontinuing to alternate power between the two linear actuators and instead apply it constantly to one of them.
The oscillatory movement of the rack gear is obtained through a transistor switching circuit of the type which is well known in the prior art. In addition to alternately switching power back and forth between the two linear actuators, the switching circuit is capable of varying the frequency at which this occurs. Thus, it is possible to vary the speed of the motor. While changing the frequency of rack gear oscillation only changes the speed of the motor when there is a pause at each end of rack gear travel, the motor can easily be configured to operate in this manner. When a motor is intended to be operated as a variable speed motor it is desirable that it comprise several stages all having their sector gears, one-way clutches and drive gears mounted on common shafts. In multiple stage motors of this type the position of the rack gear in each stage is offset from the position of the rack gear in every other stage. This causes the drive wheels to rotate continuously even though there is a pause when each individual rack gear changes direction.
Since electric linear actuators achieve their greatest force when they are almost fully retracted, the motor of the present invention has limit switches located between the actuators which are contacted by the rack gear as it travels. The limit switches are used to selectively control the distance the rack gear travels before its direction is reversed. Thus, the length the rack gear stroke can be varied. With low frequency oscillation of the rack gear, its stroke will necessarily be quite long in order to prevent large pauses at the end of each stroke. However, as the frequency of the oscillation is increased the stroke of the rack gear will be shortened in order that the actuator be operated more closely in the range where it has maximum power. Thus, frequency of oscillation and length of rack gear stroke normally are changed together in order to obtain the best combination for achieving maximum power at the desired speed. Even though the length of the rack gear stroke can be varied to achieve maximum power, the device by its very nature always operates near the end of the actuation element stroke where a high level of power is obtained from the actuators.
Accordingly, it is a principal object of the present invention to provide an electric motor which is lightweight, operates at a low speed, and has a high torque output.
It is a further object of the present invention to provide such a motor in which continuous rotary output is obtained from linear actuators.
It is a still further object of the present invention to provide such a motor which can have its direction reversed quickly without creating stress on its components that is in excess of what occurs in normal operation.
It is a yet further object of the present invention to provide such a motor which can be locked up quickly without creating stress on its components that is in excess of what occurs in normal operation.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.